Atlas Mill Achilles Heel

[JPMacG]

I seem to have found the Achilles heel of the Atlas milling machine. It is the teeth that couple the spindle pulley to the spindle small gear. They are mangled on my machine. I don't know how it happened, it predated my ownership of the machine. Without those teeth in working order I can't operate the back gear.

Clausing is sold out of those parts, and apparently they are not producing new parts for the Atlas. I can't think of a way to do a repair. I'm debating what to do. I could buy a used part on ebay for several hundred dollars. I could switch to a variable speed motor and use just the belt drive.

I'd appreciate hearing your ideas.

 

[brino]

Hi Jon,

Could you post a picture for us non-atlas guys?

If it's like the picture in my head, could you broach key ways in both parts and add some keys?
-brino

 

[wa5cab]

Jon,

The problem with replacing the back gears with a variable speed motor is two fold. First, you shift the high torque requirement upstream in the drive train which subjects parts like the direct drive pin to forces much higher than they normally see. The second is that motors have to be cooled. Mostly this is done by a fan mounted on the motor armature. It has been stated in the literature (I've read it but can't recall exactly where) that below about 30% of max RPM, the cooling efficiency of the direct coupled fan drops off rapidly. Typical maximum RPM of AC or DC variable speed motors is 1800 to 3600 RPM. 30% of even 1800 is 540. For DC motors, it will usually be higher. The direct drive speed range of the 4-speed MFC is about 450 to 2870 using a nominal 1725 RPM motor. If you keep the 2-speed spindle drive and the 2-speed motor pulley, you can almost match that with a variable speed motor running between 30% and 100%. But you can't come anywhere near matching the back gear speeds. So the moral of the story is that you should keep the back gears operational.

Just from looking at the drawings and photos, it appears that the most likely cause of the dogs on the small spindle gear and the mating slots in the spindle pulley getting badly worn is failure to properly adjust the collar (called a spacer on the parts drawings) to the left of the small spindle gear. This should be adjusted along with the bull gear such that there is minimal end float in the spindle pulley and small gear.

 

[JPMacG]

Thanks Robert. I think that is exactly how it happened. When I bought the mill I noticed that there was a gap between the spacer and the gear. When I disassembled and cleaned the spindle I noticed that the dogs had a triangular shape. They were angled such that they wanted to push the collar to the left when the back gear was engaged. I cleaned and reassembled the spindle and pushed the spacer hard to the right. But now if I put a moderate load on the cutter the force from the angled dogs overpowers the set screws and pushes the spacer to the left. Then the dogs start to grind, which makes them worse.

I'll post a photo when I get home tomorrow.

 

[wa5cab]

You're welcome. And it's probably good that you don't have the photo up yet. My mobile connection (Sprint) has devolved to less than 300 baud. Took forever to paint this screen. This may be my only message until I get back to Houston and a decent connection.

 

[spongerich]

The MFC shares a lot of parts with the Atlas 618. 618 parts are a bit more plentiful if they'll interchange.

 

[wa5cab]

Prior to about 1952, the Atlas part numbering system was pretty logical. If the part number began with M6, the part was first made for the 618. If it began with M1, MF or MH it was first made for one of the mills. If it began with S7 it was first made for the shaper. If it began with 9 or 10 it was first made for the 9" or one of the 10". And if it began with L and a number it was first made for a 12". Then the illogical Clausing system began to take over and after that, it's impossible to tell.